1. Field of the Invention
This invention relates to noise reduction, more particularly to recursive noise reduction in progressive scan display systems.
2. Background of the Invention
All video sources, such as broadcast or cable TV, VCR, digital satellite, etc., contain both spatial and temporal noise. The noise can result from transmission deficiencies, skipped recording parts on tape, high frequency electrical noise, poor source reproduction, or even errors introduced by the video equipment processing the signal. Examples of these types of errors are poor chrominance and luminance separation prior to processing, repeated analog-to-digital conversion and quantization errors.
Noise created by any or all of the above can manifest itself in several ways, all of which affect the quality of the image. Examples of noise in video include horizontal streaking, busy or "snowy" areas, large impulsive changes, or color patterning. Current approaches to reducing noise typically involve comparing values from several video fields, which are sequential. This requires extra field memories, which increase the system cost. However, some systems that perform interlace to progressive scan may already have field memories.
An interlaced format has two sequential fields of video data making up one frame, while a progressive scan system receives one complete frame of data at a time. Conversion from interlace to progressive scan typically involves storing at least one field in memory. Therefore, a method allowing use of field memories in a display system for noise reduction would be beneficial, although merely adding noise reduction could slow down the system with extra program instructions.
Therefore, a method and structure are needed that allow integration of noise reduction into display systems without increasing memory costs or causing performance problems.